Synthesis characterisation and stability of mixed aryldichalcogenide bis(diphenylphosphino)ethanenickel(II) complexes. X-ray structure of Ni(dppe)(SeC6H4S)

Article abstract of DOI:10.1016/S0277-5387(99)00191-6

Mixed chalcogenide complexes of the type Ni(dppe)(SeC₆H₄S) (dppe=bis(diphenylphosphino)ethane), Ni(dppe)(SC₅H₃NCO₂) and Ni(dppe)(EC₅H₃NE′) (E=NH, E′=O; E=E′=NH) have been prepared from the reactions of Ni(dppe)Cl₂ with the appropriate aryldichalcogen or pyridine-based compound, using Et₃N as a base. The relative solution and thermal stabilities of the above compounds, other mixed chalcogen ones, Ni(dppe)(SC₆H₄O), Ni(dppe)(SC₆H₄CO₂) and Ni(dppe)(SC₆H₄NH), and the homoleptic compounds Ni(dppe)(EC₆H₄E′) (E=E′=O, E=E′=S; R=H, Me), were established by a combination of electron impact mass spectrometry (EIMS) and fast atom bombardment (FABMS). The most stable ones were the compounds with homoleptic sulfur ligands. Elsevier Science Ltd.

Full text of DOI:10.1016/S0277-5387(99)00191-6

Polyhedron 18 (1999) 2803–2810
www.elsevier.nl/locate/poly
Synthesis characterisation and stability of mixed aryldichalcogenide
bis(diphenylphosphino)ethanenickel(II) complexes. X-ray structure of
Ni(dppe)(SeC6H4S)
b,1
b
Mary S. Thomasa, James Darkwaa , , Emmanuel Y. Osei-Twum , Luis A. Litorja Jr.
*
aDepartment of Chemistry, University of the North, Private Bag X1106, Sovenga 0727, South Africa
bResearch Institute, King Fahd University of Petroleum and Minerals, KFUPM Box 1472, Dhahran 31261, Saudi Arabia
Received 8 March 1999; accepted 25 June 1999
Abstract
Mixed chalcogenide complexes of the type Ni(dppe)(SeC6H4S) (dppe5bis(diphenylphosphino)ethane), Ni(dppe)(SC5H3NCO2) and
Ni(dppe)(EC5H3NE9) (E5NH, E95O; E5E95NH) have been prepared from the reactions of Ni(dppe)Cl2 with the appropriate
aryldichalcogen or pyridine-based compound, using Et3N as a base. The relative solution and thermal stabilities of the above compounds,
other mixed chalcogen ones, Ni(dppe)(SC6H4O), Ni(dppe)(SC6H4CO2) and Ni(dppe)(SC6H4NH), and the homoleptic compounds
Ni(dppe)(EC6H4E9) (E5E95O, E5E95S; R5H, Me), were established by a combination of electron impact mass spectrometry (EIMS)
and fast atom bombardment (FABMS). The most stable ones were the compounds with homoleptic sulfur ligands.
Science Ltd. All rights reserved.
1999 Elsevier
Keywords: Nickel(II) complexes; Crystal structure; Stability; Mass spectrometry
1. Introduction
are not stored under nitrogen. We have found that
Ni(dppe)(SC6H4NH) similarly decomposes in solution
within 24 h in the presence of air [3]. On the contrary, the
homoleptic sulfur and mixed oxo/sulfur compounds are
quite stable in solution, even when kept in contact with air.
It appears the stability of these phosphino organochal-
cogenide complexes is related to how compatible the
chalcogen orbitals are with that of the nickel. The sulfur
orbitals seem to be quite suitable for interaction with those
of the nickel, hence the stability of their compounds.
A measure of the thermal stability of these compounds
seem to be reflected in the stability of molecular ions of
Ni(dppe)(SC6H4S) and Ni(dppe)(SC6H3MeS) in the mass
spectrometer when the harsh electron impact (EI) ionisa-
tion source is used in running their mass spectra [3]. In this
project we sought to establish the generality of how the
type of chalcogen relates to the stablity, solution and
thermal, of these compounds. We also wished to establish
how the type of mass spectrometric ionisation source could
be used as a simple measure of the stability of these
compounds. To do this, we carried out the EI and the fast
atom bombardment (FAB) mass spectral studies of all new
compounds and the previously reported complexes:
Diphosphino organodichalcogenide metal complexes
have been investigated for their possible use as anti-cancer
agents [1]. Some nickel complexes of this composition are
known to catalyse the cyclotrimerisation of di-
methylacetylene dicarboxylate [2], as well as to reversibly
absorb sulfur dioxide [3]. In solution, some of the diphos-
phinonickel organodichalcogenide complexes tend to de-
compose and their stability appears to be dependent on the
chalcogen atoms present. The type of chalcogen in the
complex could also affect the ability of the compounds to
undergo the above two reactions, particularly cyclotrimeri-
sation.
The
homoleptic
oxo
complexes
Ni(dppe)(OC6H3RO)
bis(diphenylphosphino)ethane, R5H, Me) reported by
Bowmaker et al. [4] readily decomposes in solution if they
(dppe5
*Corresponding author. Present address: Department of Chemistry,
University of the Western Cape, Private Bag X17, Bellville 7535, South
Africa. Tel.: 127-21-959-3053; fax: 127-21-959-3055.
E-mail address: jdarkwa@uwc.ac.za (J. Darkwa)
1Corresponding author. This author is also a Senior author.
0277-5387/99/$ – see front matter
PII: S0277-5387(99)00191-6
1999 Elsevier Science Ltd. All rights reserved.

2804
M.S. Thomas et al. / Polyhedron 18 (1999) 2803–2810
Scheme 1.
Ni(dppe)(SC6H3RS) (R5H (1a), Me (1b) [3],
Ni(dppe)(OC6H3R9O) (R95H (2a), Me (2b) [4],
Ni(dppe)(SC6H4O) (3), Ni(dppe)(SC6H4CO2) (4) and
Ni(dppe)(SC6H3NH) (5) [2].
by Rauchfuss et al. [6]. All reactions were performed
without exclusion of air, unless otherwise stated.
IR spectra were recorded on a Nicolet 205 FT-IR or a
Perkin Elmer Spectrum 1000 FT-IR spectrometers. UV–
visible spectra were run on a Varian Cary 1E spectrometer.
1H, 13C and 31P NMR spectra were recorded on a Varian
Gemini 2000 spectrometer at 200 MHz, 50.28 MHz and
80.95 MHz respectively and referenced to residual CHCl3
for 1H (d 7.26), 13C (d 77.0) and externally to PPh3 (d
25.00) for 31P. Mass spectra were recorded on a JEOL
JMS-HX100 EBE spectrometer in the Electron Impact (EI)
or Fast Atom Bombardment (FAB) mode as described
previously [5]. Elemental analyses were performed by the
micro analytical laboratory at the University of Cape
Town, South Africa as a service.
2. Experimental
2.1. Materials and instrumentation
All solvents were analytical grade, but were dried before
use. Cyclohexane, hexane and toluene were dried over
sodium and dichloromethane over P2O5. The following
compounds were used as received from Aldrich: 2-mercap-
tonicotinic acid, 2-aminonicotinic acid and 2,3-
diaminopyridine. Thiophenol (Fluka) was also used as
2.2. Syntheses
received.
Ni(dppe)(SC6H3MeS)
Ni(dppe)(OC6H3MeO)
The
complexes
[3],
Ni(dppe)(SC6H4S),
Ni(dppe)(OC6H4O),
Ni(dppe)(SC6H4O),
2.2.1. Ni(dppe)(SeC6H4S) 6
[4],
A three necked 500 ml flask, fitted with a pressure
equalising dropping funnel and a nitrogen inlet was
thoroughly flushed with nitrogen. A solution of thiophenol
(0.21 ml, 2.00 mmol) in cyclohexane (20 ml), which had
Ni(dppe)(SC6H4CO2), and Ni(dppe)(SC6H4NH) [2] were
prepared by the literature procedures. The dilithio com-
pound, LiSeC6H4SLi, was generated in situ as described

M.S. Thomas et al. / Polyhedron 18 (1999) 2803–2810
2805
previously been degassed, was slowly added dropwise to a
nitrogen saturated solution of N,N,N9N9-tetramethyl-
ethylenediamine (TMEDA) (0.8 ml) and n-butyllithium
(2.80 ml, 4.00 mmol) in cyclohexane (30 ml) at 08C. After
the addition was complete, the reaction mixture was stirred
at 08C for 30 min and gradually allowed to warm up to
room temperature, and stirred for a further 22 h. This was
followed by the addition of selenium (0.16 g, 2.00 mmol)
and stirred till all the selenium had dissolved, ca. 20 h. A
degassed solution of Ni(dppe)Cl2 (1.06 g, 2.00 mmol) in
CH2Cl2 (50 ml) was added dropwise via the pressure
equalising dropping funnel and stirred for 8 h. Addition of
hexane to the resultant solution gave a brown solid, which
was recrystallised from CH2Cl2 /hexane to give
Ni(dppe)(SeC6H4S). Yield50.33 g, 25%; melting point5
298–3008C. Anal. Calc. for C32H28PSSeNi?CH2Cl2: C,
54.36; H, 4.15; S, 4.40%. Found: C, 54.34; H, 4.19; S,
4.11%. 1H NMR (CDCl3): d 7.78 (m, 8H); 7.48 (m, 12H)
(dppe); 7.16 (d, 1H, JHH 57.80 Hz); 6.90 (m, 3H)
(SSeC6H4); 2.36 (m, 4H) (dppe). 13Ch1Hj NMR: d 134.3
(s), 132.5 (s), 132.2 (t, JCP 55.38 Hz), 131.6 (s), 130.9 (s),
130.2 (s), 129.5 (t, JCP 56.08 Hz), 129.9 (s), 125.4 (s), 26.8
(t, JCP 524.78 Hz). 31Ph1Hj NMR: d 59.8 (d, P trans S,
JPP 543.59 Hz); 58.7 (d, P trans Se). MS (EI): 644 (M1,
45), 430 (10), 398 (100), 370 (32), 353 (78), 289 (70),
262 (82), 185 (63), 183 (89), 108 (20), 77 (10). MS
(FAB1): 644 (M1, 25). IR (KBr pellet cm21): 3036w,
2882w, 1602m, 1475s, 1433vs, 1406w, 1313w, 1288w,
1195w, 1173m, 1100vs, 1067w, 1026w, 998w, 955m,
875w, 845w, 804w, 755m, 728vs, 692vs, 531vs, 495s,
479m, 430w.
(dppe). 31Ph1Hj NMR: d 58.0 (d, P trans S, JPP 562.86
Hz); 43.5 (d, P trans O). MS (FAB1): 609 (M1, 100).
U.V.–vis (CH2Cl2): lmax 5418 nm. IR (KBr pellet, cm21):
3043w, 2945w, 1605vs, 1570vs, 1485s, 1436vs, 1387vs,
1346vs, 1184w, 1146s, 1100vs, 1078m, 1028w, 1001m,
867s, 826s, 758vs, 706s, 687s, 531vs, 490s, 476m, 446w,
424w.
2.2.3. Ni(dppe)(HNC5H3NO)?1/2CH2Cl2 8
Ni(dppe)(HNC5H3NO)?1/2CH2Cl2 8 was prepared and
isolated a light purple solid via the procedure described for
7, using Ni(dppe)Cl2 (0.53 g, 1.00 mmol) and 2-amino-
nicotinic acid (0.11 g, 1.00 mmol). Yield50.24 g, 43%;
melting
point5229–2328C.
Anal.
Calc.
for
C31.5H28ClN2OP2Ni: C, 62.26; H, 4.81; N, 4.61%. Found:
C, 62.52; H, 5.15; N, 4.67%. 1H NMR (CDCl3): d 7.97 (t,
4H, JHH 59.50 Hz); 7.84 (m, 4H); 7.53(m, 12H) (dppe);
6.75 (s, br, NH); 6.52 (d, 1H, JHH 57.40 Hz); 6.11 (t, 2H,
J
HH 56.60 Hz); (HNC5H3NO); 2.31 (m, 4H) (dppe).
13Ch1Hj NMR: d 160.4 (s), 133.4 (d JCP 510.66 Hz); 132.
(d, JCP 521.02 Hz); 130.1 (dd, JCP 523.26 Hz, JCP9 510.69
Hz) (dppe); 129.3 (s), 128.4 (s), 128.1 (s), 127.1 (s),
118.6(s) (HNC5H3NO); 27.4 (dd, JCP 536.25 Hz, JCP9
5
13.53 Hz); 24.5 (dd, JCP 535.85 Hz, JCP9 511.82 Hz)
(dppe). 31Ph1Hj NMR: d 60.1 (d, P trans N, JPP 572.61
Hz); 53. 0 (d, P trans O). MS (FAB1): 566 (M1, 100).
U.V.–vis (CH2Cl2): lmax 5374 nm. IR (KBr pellet, cm21):
3395w, 3219w, 3050w, 2910w, 1619s, 1597vs, 1540vs,
1482s, 1433vs, 1351s, 1283vs, 1250s, 1187m, 1100vs,
1067w, 1026m, 999m, 897m, 873s, 859m, 818m, 774m,
744vs, 725vs, 706vs, 689vs, 654m, 624s, 528vs, 492s,
479s, 446w.
2.2.2. Ni(dppe)(SC5H3NCO2 ) 7
2.2.4. Ni(dppe)(HNC5H3NNH)?CH2Cl2 9
To a solution of Ni(dppe)Cl2 (1.00 g, 1.89 mmol) and
2-mercaptonicotinic acid (0.29 g, 1.89 mmol) in CH2Cl2
(50 ml) was added Et3N (1 ml). On addition of Et3N, the
mercaptonicotinic acid started to dissolve and the mixture
was stirred for 4 h. Hexane was added to the resultant
solution to give a dark orange precipitate, which was
washed with copious amount of water to remove Et3NHCl.
The product was recrystallised from CH2Cl2 /hexane, after
a CH2Cl2 solution was dried over anhydrous Na2SO4
Ni(dppe)(HNC5H3NNH)?CH2Cl2 9 was prepared and
isolated as described for 7, using Ni(dppe)Cl2 (0.53 g, 1.00
mmol) and 2,3-diaminopyridine (0.11 g, 1.00 mmol).
Yield50.29 g, 52%. Anal. Calc. for C31H28ClN3P2Ni: C,
62.26; H, 4.81; N, 4.61%. Found: C, 62.52; H, 5.15; N,
4.67%. 1H NMR (CDCl3): d 7.98 (m, 4H); 7.81 (m, 4H);
7.52 (m, 12H) (dppe); 6.71 (t, 1H, JHH 55.40 Hz); 6.51 (s,
br, NH); 6.24 (d, 1H, JHH 57.20 Hz); 6.07 (t, 1H, JHH 5
6.60 Hz); 3.53 (s, br, 1H) (HNC5H3NNH); 2.29 (m, 4H)
(dppe). 31Ph1Hj NMR: d 63.8 (d, P trans N, JPP 557.48
Hz); 60.5 (d, P trans N). MS (FAB1): 564 (M1, 100).
U.V.–vis (CH2Cl2): lmax 5398 nm. IR (KBr pellet, cm21):
3065w, 2903w, 1603m, 1537s, 1485m, 1433vs, 1381w,
1310s, 1264w, 1187s, 1173w, 1124w, 1100vs, 1075w,
1023w, 998m, 900w, 875m, 821s, 818m, 747w, 728w,
714w, 706w, 692vs, 657w, 643w, 613w, 533vs, 512w,
482s, 442w.
overnight,
to
give
analytically
pure
Ni(dppe)(SC5H3NCO2). Yield50.92 g, 79%; melting
point5254–2568C. Anal. Calc. for C32H27NO2P2SNi: C,
62.98; H, 4.46; N, 2.30; S, 5.25%. Found: C, 62.71; H,
1
4.51; N, 2.36; S, 5.14%. H NMR (CDCl3): d 8.36 (dd,
1H, JHH 57.80 Hz, JHH 52.00 Hz); 8.25 (dd, 1H, JHH 5
4.50 Hz, JHH 52.10 Hz); 6.88 (dd, 1H, JHH 57.70 Hz,
J
HH 54.60 Hz), (SC5H3NCO2); 2.42 (m, 2H); 2.09 (m,
2H) (dppe). 13Ch1Hj NMR: d 150.0 (s), 140.7 (s), 118.6 (s)
(SC5H3NCO2); 134.0 (dd JCP 524.43 Hz, JCP9 510.31
Hz); 132.5 (dd, JCP 524.40 Hz, JCP9 52.67 Hz); 129.9 (dd,
2.3. Crystal structure determination of 6
JCP 510.51 Hz, JCP9 56.69 Hz); 29.5 (dd, JCP 535.08 Hz,
JCP9 517.93 Hz); 22.4 (dd, JCP 531.68 Hz, JCP9 510.31 Hz)
Single crystals of 6 were obtained from a 2:1 CH2Cl2 /

2806
M.S. Thomas et al. / Polyhedron 18 (1999) 2803–2810
hexane solution at 2158C. A dark rectangular crystal of
size 0.6230.5030.30 mm was mounted in a sealed
capillary tube for data collection. All geometric and
intensity data were collected on a Siemens SMART
diffractometer with a CCD detector. A total of 17 646
reflections (of which 6633 [R(int)50.0394] were unique)
in the range 3.76,2u ,56.568 were collected at 296 K
with monochromatic MoKa radiation (l.50.71073 A).
Absorption correction based on multiple redundant data
analysis was applied [7].
air compared to the mixed sulfur and selenium compound
was very low. A similar route was used to prepare the
tellurium complex, which had a much lower stability than
that of the selenium complex. The selenium and tellurium
complexes could be characterised from their 31P NMR
spectra; which gave singlets at 36.56 and 33.93 ppm
respectivley. These peak values are indicative of the effect
of the electronegativity of the chalcogen. The relative
stabilities of these complexes could be established by
leaving solutions of the compounds in CH2Cl2. Whereas
solutions of 6 could be left in air for more than a day, the
diselenato complex rapidly decomposed in air with 1H
NMR signals of the latter disappearing within 24 h.
The stability of these complexes appears to be de-
termined by the compatibility of the metal orbitals with the
chalcogen. The more stable compounds, in solution, were
the dithiolato, Ni(dppe)(SC6H4RS) (R5H, Me) [3] and the
mixed oxo-sulfido compounds, Ni(dppe)(SC6H4O) and
Ni(dppe)(SC6H4CO2) [2]. Synthesis of the dithiolato and
the mixed oxo-sulfido compounds could even be per-
formed in the presence of air. When the chalcogens were
sulfur and selenium, though the reaction had to be per-
formed in an inert atmosphere, work-up and subsequent
storage in air showed that the product was quite stable. On
the other hand, solutions of Ni(dppe)(SeC6H4Se), and the
previously reported Ni(dppe)(SC6H4NH) [2] and
Ni(dppe)(OC6H3RO) (R5H, Me) [4], decomposed when
exposed to air. These observations point to a link between
the strength of the Ni–chalcogen interactions, with Ni–S
being the most stable.
˚
Crystal data: C32H28P2SSeNi: monoclinic, P21 /c; a5
˚
˚
˚
11.205(5) A, b520.331(9) A, c513.936(6) A, b5
3
˚
113.356(10)8, V52914.5(2) A ; Z54.
The structure was solved by the Patterson method for
primary atom sites and by difference map for atoms in
secondary sites [8]. All non-hydrogen atoms were refined
anisotropically and hydrogen atoms were refined without
restraints. Full-matrix least squares refinement [9] of 334
parameters on F2 gave R1 50.0770, wR2 50.2273, with a
weighting scheme of w21 5 s2(Fo2) 1 (0.100P)2 1 0.00P,
where P 5 (Fo2 1 2Fc2)/3. Goodness-of-Fit51.591. Max
23
23
˚
˚
DF 2.046 e A , min 22.170 e A
.
3. Results and discussion
3.1. Syntheses and stabilities of complexes
The mixed sulfur–selenium complex was obtained from
the reaction of in situ generated LiSeC6H4SLi with
Ni(dppe)Cl2 (Eq. (1)).
By reacting 2-mercaptonicotinic acid, 2-aminonicotinic
acid
and
2,3-diaminopyridine
respectively
with
Ni(dppe)Cl2 in the presence of Et3N, similar complexes
were isolated. Because the pyridine-based ligands were
insoluble in toluene, the reactions were carried out in
CH2Cl2. The ligands were only sparingly soluble in this
solvent but the reactions were complete within 24 h. These
reactions could also be performed in the presence of air.
There was a clear indication of the effect of the nitrogen-
based ring on the stability of these compounds. This could
be established from the EI and FAB mass spectra; with the
FAB spectra showing molecular ions whilst the EI spectra
had no molecular ions. Whereas several of the phenyl-
based ligands showed molecular ions in their EI mass
spectra, the complexes with the pyridine-based ligands had
no molecular ions. Their molecular ions could only be
observed in their FAB spectra. Details of the mass spectral
study are discussed latter.
(1)
The complex was isolated as a microcrystalline solid and
characterised by a combination of IR, NMR and micro-
analysis. In addition to peaks of the phosphine, the 1H
NMR spectrum showed a downfield doublet at 7.16 ppm
for the proton ortho to the sulfur; while the rest of the
protons of the ligand appeared as a multiplet at 6.90 ppm.
The 31P NMR spectrum is discussed, together with those
of the other complexes, later in this report. X-ray diffrac-
tion studies confirmed that the SeSC6H4 binds to the
nickel as a bidentate ligand.
4. 31P NMR characterization of complexes
The 31P NMR spectra of CDCl3 solutions of all com-
pounds were run at room temperature. All the mixed-
ligand complexes displayed spectra of two doublets, with
an AB or AX spin pattern (Table 1); whilst the homochal-
The diselenato analogue was also prepared via the
reaction of in situ generated LiSeC6H4SeLi with
Ni(dppe)Cl2; but its stability in solution when exposed to

M.S. Thomas et al. / Polyhedron 18 (1999) 2803–2810
2807
Table 1
31P NMR Spectra of (dppe)Ni aryldiorganochalcogenides
Complex
Chemical Shift (ppm)
JPP Hz
D ppm
Ref.
Ni(dppe)(SC6H4S)
Ni(dppe)(SC6H3MeS)
Ni(dppe)(SC6H4O)
s, 58.45
s, 58.62
d, 58.88, 47.97
d, 59.83, 58.72
s, 36.56
–
–
0
0
[4]
[4]
[3]
This work
This work
This work
[3,10]
This work
[3]
This work
This work
54.95
43.59
–
10.91
1.11
0
Ni(dppe)(SC6H4Se)
Ni(dppe)(SeC6H4Se)
Ni(dppe)(TeC6H4Te)
Ni(dppe)(SC6H4CO2)
Ni(dppe)(SC5NH3CO2)
Ni(dppe)(SC6H4NH)
Ni(dppe)(HNC5H3NO)
Ni(dppe)(HNC5NH3NH)
s, 33.93
–
0
d, 57.19, 41.72
d, 57.98, 43.47
d, 60.44, 59.77
d, 60.14, 52.94
d, 63.80, 60.55
59.90
62.86
47.56
72.61
57.48
15.47
14.51
0.67
7.20
3.25
cogenide complexes of Se and Te gave singlets typical of
such compounds [3]. Complexes 7 and 8, which contain
oxygen, gave AX spectra quite similar to those of
Ni(dppe)(SC6H4O) [2] and Ni(dppe)(SC6H4CO2) [2,10].
The non-oxygen containing complexes, 6 and 9, had AB
spectra also similar to that of Ni(dppe)(SC6H4O) [2]. The
chemical shifts of the doublets associated with each of the
phosphorus atom of the dppe ligand can be linked to the
trans-influence of the chalcogen atom trans to the phos-
phorus. The more polarisable chalcogen has a better trans-
influence. For example in complex 7, the chemical shift of
the phosphorus trans to the S was 58.0 ppm, whilst the
phosphorus trans to the less polarisable oxygen atom was
43.5 ppm. Trans-influence of chalcogens on 31P NMR was
first
observed
by
Henderson
et
al.
for
Pt(dppe)(SC6H4CO2) [10]. Even for the homoleptic com-
Fig. 1. Molecular structure of complex 6.

2808
M.S. Thomas et al. / Polyhedron 18 (1999) 2803–2810
plex, Ni(dppehS2C2(2-pyridine)(H)j) [11], the influence of
the pyridine nitrogen results in different electronic environ-
ment similar to that produced by the polarisability differ-
ences described above. This results in two broad singlets
(57.4 and 57.2 ppm) for the dppe phosphorus in
Ni(dppehS2C2(2-pyridine)(H)j). It is evident from our
results that the trans-influence is more pronounced when
one of the chalcogens is oxygen and leads to an AX
spectrum. It also appears that 31P NMR spectroscopy can
be used as a measure of the trans-influence of atoms. The
data in Table 1 seem to indicate that the NH unit, which is
isoelectronic with oxygen, has a better trans-influence than
oxygen.
longer
bond
distances,
such
as
in
the
Ni(II)diethyldithiocabarmate phenylselenide complex,
Ni(dtc)(PPh3)(SeC6H5)
(2.317(2) A) [14] and Ni(h -C5H5)(PPh3)(SeC6H4Cl-4)
(2.317(6) A) [15]. On the other hand, the Ni–S bond
distances (2.236(6) A) and 2.273(2) A) are longer than
similar bonds found in Ni(dppe)(SC6H4O) (2.158(1) A)
[2] and Ni(dppe)(SC6H4S) (2.145(2) A) [3].
It is clear from the Ni-chalcogen distances that the
disorder affects the Ni–chalcogen interactions. The S–Ni–
Se bite angles (92.46(8)8) and 94.3(2)8) though, are quite
similar to those found in Ni(dppe)(SC6H4O) (94.3(2)8) [2]
and Ni(dppe)(SC6H4S) (92.4(1)8) [3]. All other bond
parameters of 6 are comparable with literature values. The
crystal structure thus allows a complete characterisation of
the complex and hence a basis for the full interpretation of
its mass spectrum.
(dtc5diethyldithiocabarmate)
5
˚
˚
˚
˚
˚
˚
4.1. Molecular structure of Ni(dppe)(SeSC6H4 )
The coordination geometry about the nickel atom is
essentially square planar. The S and Se positions of the
mixed dichalcogenide ligand appears to be disordered, thus
the exact positions of these atoms could not be established.
Fig. 1 gives an ORTEP view of molecule, which clearly
depicts the disorder. This resulted in two possible positions
and their related bond distances and angles. Table 2 gives
selected bond distances and angles of the molecule. The
4.2. Electron impact and fast atom bombardment mass
spectrometric study
In a previous study we investigated the effectiveness of
electron impact (EI) and fast atom bombardment (FAB)
ionisation techniques in characterising nickel–thiolate
complexes [5]. None of the complexes in that study
showed any molecular ions in the EI spectra, whereas the
FAB spectra had the molecular ions of the compounds. In
the present study, we investigated the complexes that
contained ligands with a combination of oxygen, sulfur,
selenium or nitrogen bound to the nickel. Our general
observation was that most of the complexes with sulfur as
one of the two binding atoms gave molecular ions when
either EI or FAB was used. Three of the complexes studied
(4, 5 and 7), with sulfur containing ligands, gave no
molecular ions in the EI mode. Two of these, 4 and 7,
readily lost CO2 even in the FAB mode (Fig. 2), and could
explain why the harsh EI source produced no molecular
ions. Complex 5 was found to be unstable in solution [2]
and came as no surprise when the EI spectrum had no
molecular ion. In addition to complexes 4, 5 and 7, two
other complexes (8 and 9) had no molecular ions. How-
ever, all complexes had molecular ions when the softer
FAB ionisation method was used.
˚
Ni–Se bond distances of 2.256(2) and 2.217(2) A for the
two possible Se sites are only slightly shorter than the
bonds in [Ni(Se2C6H4)2]2 (2.270(5) A) [12] and
˚
˚
Ni(SeP(Ph)2C6H4)2 (2.280(3) A) [13]. Other Ni–Se dis-
tances with the nickel in a 12 oxidation state show even
Table 2
Selected bond distances and angles for 6
˚
Bond distances (A)
Ni–S(1)
Ni–Se(1)
Ni–P(1)
2.263 (6)
2.256 (2)
2.160 (2)
1.861 (8)
1.851 (6)
1.834 (6)
1.841 (6)
1.821 (6)
Ni–S(2)
Ni–Se(2)
Ni–P (2)
S(2)–C(5)
Se(2)–C(4)
P(1)–C(101)
P(2)–C(71)
P(2)–C(12)
2.273 (2)
2.217 (2)
2.173 (2)
1.939 (7)
1.775 (7)
1.811 (6)
1.801 (6)
1.863 (6)
1.424 (9)
1.385 (9)
S(1)–C(4)
Se(1)–C(5)
P(1)–C(91)
P(1)–C(11)
P(2)–C(81)
C(2)–C(3)
C(4)–C(5)
C(11)–C(12)
1.330 (11) C(3)–C(4)
1.392 (9)
1.534 (8)
C(5)–C(6)
–
–
The dithiolato complexes, 1a and 1b, were observed to
be the most stable with EI ionisation. They gave molecular
ions of relative intensities of 60% and 75% respectively.
The mixed ligands, sulfur/selenium and sulfur/oxygen,
were observed to have molecular ions with 50% inten-
sities. A typical fragmentation pattern for this type com-
pounds is shown by the mixed sulfur/selenium compound
(Fig. 3 and Scheme 1). Apart from the molecular ion, there
was an ion at m/z5596, which was assigned to the more
stable Ni(dppe)(SC6H4S). Since this product was found
only in the EI spectrum, it must have resulted from the
rearrangement of 6 in the ionisation chamber. Other
Bond distances (8)
P(1)–Ni(1)–P(2)
P(2)–Ni(1)–Se(2)
P(2)–Ni(1)–S(1)
P(1)–Ni(1)–Se(1)
Se(2)–Ni(1)–Se(1)
P(1)–Ni(1)–S(2)
Se(2)–Ni(1)–S(2)
Se(1)–Ni(1)–S(2)
86.60 (6)
89.48 (8)
88.2 (2)
91.85 (6)
92.46 (8)
90.60 (11)
94.18 (12)
7.15 (12)
P(1)–Ni(1)–Se(2)
P(1)–Ni(1)–S(1)
Se(2)–Ni(1)–S(1)
P(2)–Ni(1)–Se(1)
S(1)–Ni(1)–Se(1)
P(2)–Ni(1)–S(2)
S(1)–Ni(1)–S(2)
173.98 (7)
166.84 (14)
7.6 (2)
174.66 (16)
94.3 (2)
167.53 (11)
96.9 (2)
C(101)–P(1)–C(11) 105.6 (3)
C(101)–P(1)–C(91) 104.1 (13)
C(91)–P(1)–C(11)
C(91)–P(1)–Ni(1)
C(71)–P(2)–Ni(1)
C(12)–P(2)–Ni(4)
102.5 (3)
112.6 (2)
116.8 (2)
109.8 (2)
C(101)–P(1)–Ni(1)
C(11)–P(1)–Ni(1)
C(81)–P(2)–Ni(1)
123.2 (2)
106.9 (2)
114.4 (2)

M.S. Thomas et al. / Polyhedron 18 (1999) 2803–2810
2809
Fig. 2. FAB mass spectrum of complex 4.
fragment ions resulting from the molecular ions or the ions
5. Conclusions
therefrom were also observed in the EI spectrum. These
have been provisionally assigned ionic structures as:
[(dppe)S]1 (m/z5430), [dppe]1 (m/z5398), [(ppe)S]1
(m/z5353) (ppe5phenylphosphinoethane), [PPh3]1 (m/
z5262) and sequential loss of phenyl groups (Ph2P m/z5
183 and Ph m/z577). Both the EI and FAB spectra of
these complexes show that they are dominated by frag-
mentation of the dppe ligand.
The stability of the bis(diphenylphosphino)nickel(II)
complexes described above depend on the nature of the
chalcogen. This appears to be determined by the size of the
chalcogen atom and hence the atom’s effective overlap
with the nickel. The small oxygen and the larger selenium
and tellurium atoms form less stable complexes compared
to the sulfur ones. The stability of mixed oxo/sulfur and
Fig. 3. EI mass spectrum of complex 6.

2810
M.S. Thomas et al. / Polyhedron 18 (1999) 2803–2810
sulfur/selenium ligand complexes is quite good compared
to the homoleptic oxo or selenium analogues.
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Acknowledgements
Financial support from the Foundation for Research
Development, South Africa (J.D.), University of the North
and the Research Institute, King Fahd University of
Petroleum and Minerals is gratefully acknowledged. We
are also grateful to Professor J.C.A. Boeyens and Ms.
Leanne Cook, Structural Chemistry Department, Universi-
ty of the Witwatersrand, South Africa, determining the
crystal structure as a service.